title: Deposition of uranium precipitates in dolomitic gravel fill.
abstract: Uranium-containing precipitates have been observed in a dolomitic gravel fill near the Department of Energy (DOE) S-3 Ponds former waste disposal site as a result of exposure to acidic (pH 3.4) groundwater contaminated with U (33 mg L(-1)), Al3+ (900 mg L(-1)), and NO3- (14 000 mg L(-1)). The U containing precipitates fluoresce a bright green under ultraviolet (UV) short-wave light which identify U-rich coatings on the gravel. Scanning electron microscopy (SEM) microprobe analysis show U concentration ranges from 1.6-19.8% (average of 7%) within the coatings with higher concentrations at the interface of the dolomite fragments. X-ray absorption near edge structure spectroscopy (XANES) indicate that the U is hexavalent and extended X-ray absorption fine structure spectroscopy (EXAFS) shows that the uranyl is coordinated by carbonate. The exact nature of the uranyl carbonates are difficult to determine, but some are best described by a split K(+)-like shell similar to grimselite [K4Na(UO2)(CO3)3 x H2O] and other regions are better described by a single Ca(2+)-like shell similar to liebigite [Ca2(UO2)(CO3)3 x 11(H2O)] or andersonite [Na2CaUO2(CO3)3 x 6H2O]. The U precipitates are found in the form of white to light yellow cracked-formations as coatings on the dolomite gravel and as detached individual precipitates, and are associated with amorphous basalumnite [Al4(SO4)(OH)10 x 4H2O].
authors.affiliation: Environmental Engineering Research Centre, School of Planning, Architecture, and Civil Engineering, Queens University of Belfast, Belfast BT9 5AG, Northern Ireland, UK.
authors.forename: D H
authors.initials: DH
authors.lastname: Phillips
authors.forename: D B
authors.initials: DB
authors.lastname: Watson
authors.forename: S D
authors.initials: SD
authors.lastname: Kelly
authors.forename: B
authors.initials: B
authors.lastname: Ravel
authors.forename: K M
authors.initials: KM
authors.lastname: Kemner
mesh_terms: D000143:Acids; D002119:Calcium Carbonate / Q000737:chemistry*; D002254:Carbonates / Q000737:chemistry; D011232:Chemical Precipitation; D008274:Magnesium / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D012987:Soil; D013057:Spectrum Analysis; D014501:Uranium / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000737:chemistry; D014881:Water Supply
chemical_list: D000143:Acids; D002254:Carbonates; D012987:Soil; D014875:Water Pollutants, Radioactive; D014501:Uranium; D002119:Calcium Carbonate; D008274:Magnesium; C028042:calcium magnesium carbonate